4′-thio-L-xylofuranosyl nucleosides, precursors thereof, preparation and use thereof

ABSTRACT

Compounds represented by the formula 1: 
                 
 
     A is selected from the group consisting of 
                 
         wherein each R individually is H or acyl, Y is X, N 3 , NH 2 , monoalkylamino, or dialkylamino; Z is O or S; and   X is selected from the group consisting of hydrogen, halo, hydroxy, alkoxy, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, amino, monoalkylamino, dialkylamino, thioaryl, thioalkyl, allylamino, cyano and nitro; tautomers thereof; and pharmaceutically acceptable salts thereof are provided along with methods for their fabrication. Various of these compounds can be used as anticancer agents, or antiviral agents or to inhibit DNA replication.

This application is a continuation of PCT/US01/07323 filed Mar. 8, 2001,which claims benefit of Ser. No. 60/187,867 filed Mar. 8, 2000.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was supported by Grant CA-34200 from National Institutesof Health.

TECHNICAL FIELD

The present invention relates to new 4′-thio-L-xylofuranosyl nucleosidesand precursors thereof. Compounds employed according to the presentinvention have exhibited good anticancer activity and good antiviralactivity. The present invention is concerned with treating patients inneed of an antiviral agent by administering to the patient certain4′-thio-L-xylofuranosyl compounds. The present invention also relates toa new process for preparing the compounds employed according to thepresent invention.

BACKGROUND OF INVENTION

A large amount of research has been conducted over the years related todeveloping treatments against cancer and viral diseases. Some of thisresearch has been successful in finding clinically approved treatments.Nevertheless, efforts continue at an ever-increasing rate in view of theextreme difficulty in uncovering promising antiviral and anticancertreatments. For example, even when a compound is found to have antiviralor anticancer activity, there is no predictability of it being selectivein humans against virus or cancer cells.

Of the DNA viruses, those of the Herpes group are the source of the mostcommon viral illnesses in man. the group includes herpes simplex virus(HSV), varicella zoster virus (VZV), and cytomegalovirus (CMV). Most ofthese viruses are able to persist in the host cells; once infected,individuals are at risk of recurrent clinical manifestations ofinfection, which can be both physically and psychologically disabling.Infections with human cytomegalovirus (HCMV) are apparently ubiquitousin the general population. The virus may produce an acute disseminatedinfection in neonates and such generalized infection is often fatal.Congenital infections in children with HCMV may result in neurologicaldamage and may later result in severe auditory defects and mentalretardation. While infection is usually asymptomatic in normal adultindividuals, primary HCMV infection or reactivation of latent HCMVinvention can cause serious, life threatening disease inimmunosuppressed patients.

SUMMARY OF INVENTION

It has been found according to the present invention that certainthioxylofuranosyl cytosine compounds are suitable as anticancer agentsand antiviral agents.

More particularly, the present invention relates to compoundsrepresented by the formula 1:

-   -   wherein each R individually is H, an alkyl group, or an acyl        group;    -   A is selected from the group consisting of    -   wherein Y is X, N₃, NH₂, monoalkylamino, or dialkylamino; Z is O        or S; and    -   X is selected from the group consisting of hydrogen, halo,        hydroxy, alkoxy, alkyl, haloalkyl, alkenyl, haloalkenyl,        alkynyl, amino, monoalkylamino, dialkylamino, thioaryl,        thioalkyl, allylamino, cyano and nitro; tautomers thereof; and        pharmaceutically acceptable salts thereof.

It has also been found according to the present invention that theabove-disclosed compounds of formula 1 can be used to inhibit DNAreplication in a mammalian cell by contacting the cell with at least oneof these compounds.

The present invention also relates to pharmaceutical compositionscontaining the above disclosed compounds of formula 1 in amountseffective as anticancer or antiviral agents.

Furthermore, the present invention relates to treating a patient in needof an anticancer agent or antiviral agent by administering to thepatient an anticancer or antiviral effective amount of a compound offormula 1.

The present invention also relates to preparing the above compounds. Inparticular, compounds of the present invention can be prepared asfollows:

A. reacting a 2,3,5 tri-O-aryl or O-alkyl-D-arabinofuranoside withbenzyl mercaptan in the presence of stannic chloride to produce thecorresponding dithioacetal such as 2,3,5-tri-O-benzyl-D-arabinosedibenzyl dithioacetal;

B. subjecting the product from A to cyclization converting the D-arabinoto the corresponding L-xylo compound such as 2,3,5-tri-O-benzyl dithioL-xylofuranoside;

C. subjecting the product from B to acidolysis to form the correspondingO-acetyl-4-thio-L-xylofuranose such as2,3,5-tri-O-benzyl-1-O-acetyl-4-thio-L-xylofuranose;

D. subjecting the product from C to reaction with dichloropurine to formthe corresponding dichloropurine compound such as9-(2,3,5-tri-O-benzyl-4-thio-α andβ-L-xylofuranosyl)-2,6-dichloropurine;

E. subjecting the product from D to reaction with ammonia to produce thecorresponding 2-chloroadenine nucleoside;

F. subjecting the product from E to removal of the O-aryl or O-alkylgroup to form for example 2-chloro-9-(4-thio-α-L-xylofuranosyl) adenine;or 2-chloro-9-(4-thio-β-L-xylofuranosyl) adenine;

G. subjecting the product from D to reaction with an azide to form thecorresponding diazide;

H. reducing the diazide from G to form the corresponding diamino purinecompound; and

I. optionally deblocking the diamino purine from H to form thecorresponding diamino nucleoside; and

J. optionally converting the diamino nucleoside from I to thecorresponding guanine nucleoside; or

K. coupling the product from B with thymine, uracil or cytosine orsubstituted analogs thereof; and

L. optionally deblocking the coupled product from K to provide thecorresponding nucleoside.

Still other objects and advantages of the present invention will becomereadily apparent by those skilled in the art from the following detaileddescription, wherein it is shown and described only the preferredembodiments of the invention, simply by way of illustration of the bestmode contemplated of carrying out the invention. As will be realized theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects,without departing from the invention. Accordingly, the descriptioncontained herein is to be regarded as illustrative in nature and not asrestrictive.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

The present invention relates to compounds represented by the formula 1:

-   -   wherein each R individually is H, or an acyl group.

The compounds of the present invention include those wherein all three Rgroups are the same, or wherein at least one group differs from theothers, or wherein all three differ including different acyl groups.

-   -   A is selected from the group consisting of:

wherein Y is X, N₃, NH₂, monoalkylamino, or dialkylamino; Z is O or S,and X is selected from the group consisting of hydrogen, halo, hydroxy,alkoxy, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, amino,monoalkylamino, dialkylamino, thioaryl, thioalkyl, allylamino, cyano andnitro; tautomers thereof; and pharmaceutically acceptable salts thereof.

Suitable alkyl groups for X typically contain 1-6 carbon atoms and canbe straight or branched chain. Some examples are methyl, ethyl,i-propyl, n-propyl, i-butyl, n-butyl, pentyl and hexyl.

Suitable acyl groups include acetyl, benzoyl and toluoyl.

Suitable halogen groups for X include Cl, Br and F.

Suitable alkoxy groups typically contain 1-6 carbon atoms and includemethoxy, ethoxy, propoxy and butoxy.

Suitable haloalkyl groups typically contain 1-6 carbon atoms and can bestraight or branched chain and include Cl, Br or F substituted alkylgroups including the above specifically disclosed alkyl groups.

Suitable alkenyl groups typically contain 2-6 carbon atoms and includeethenyl and propenyl.

Suitable haloalkenyl groups typically contain 1-6 carbon atoms andinclude Cl, Br or F substituted alkenyl groups including the abovespecifically disclosed alkenyl groups.

Suitable alkynyl groups typically contain 1-6 carbon atoms and includeethynyl and propynyl.

Suitable monoalkylamino groups for X contain 1-6 carbon atoms andinclude monomethylamino, monoethylamino, mono-isopropylamino,mono-n-propylamino, mono-isobutyl-amino, mono-n-butylamino,mono-n-hexylamino and monocyclopropylamino. The alkyl moiety can bestraight or branched chain.

Suitable dialkylamino groups for Y and X contain 1-6 carbon atoms ineach alkyl group. The alkyl groups can be the same or different and canbe straight or branched chain. Examples of some suitable groups aredimethylamino, diethylamino, ethylmethylamino, dipropylamino,dibutylamino, dipentylamino, dihexylamino, methylpentylamino,ethylpropylamino and ethylhexylamino.

Preferred compounds according to the present invention include:

-   2-chloro-9-(4-thio-α-L-xylofuranosyl) adenine;-   2-chloro-9-(4-thio-β-L-xylofuranosyl) adenine;-   9-(2,3,5-tri-O-benzyl-4-thio-α,    L-xylofuranonyl)-9H-purine-2,6-diamine;-   9-(2,3,5-tri-O-benzyl-4-thio-β,    L-xylofuranosyl-9H-purine-2,6-diamine;-   9-(4-thio-α-L-xylofuranosyl)-9H-purine-2,6-diamine;-   9-(4-thio-β-L-xylofuranosyl)-9H-purrine-2,6-diamine;-   9-(4-thio-β-L-xylofuranosyl) guanine;-   1-(2,3,5-tri-O-benzyl-4-thio-α, β-L-xylofuranosyl) thymine;-   1-(2,3,5-tri-O-benzyl-4-thio-α, β-L-xylofuranosyl) uracil;-   1-(4-thio-α, β-L-xylofuranosyl)thymine;-   1-(4-thio-α, β-L-xylofuranosyl)uracil.;-   1-(2,3,5-tri-O-benzyl-4-thio-α,β-L-xylofuranosyl)cytosine; and-   1-(4-thio-α,β-L-xylofuranosyl)cytosine.    Compounds of the present invention can be prepared by following the    reaction schemes illustrated in Scheme A below and the specific    examples which illustrate preparing preferred compounds of the    present invention to facilitate an understanding of the present    invention. For instance, methyl    2,3,5-tri-O-benzyl-D-arabinofuranoside (3) can be prepared by known    two steps procedure starting with arabinose. Conversion to dibenzyl    dithioacetal can be accomplished by employing benzyl mercaptan and    stannic chloride. A 63% yield after chromatographic purification was    achieved. Cyclization at C-4 involving a single inversion, thus    converting the D-arabino to the L-xylo configuration, was    accomplished employing triphenylphosphine, iodine, and imidazole in    72% yield. The final step, replacement of the benzylthio group at    C-1 by an acetoxy group, involved treatment of 5 with mercuric    acetate in acetic acid at room temperature. The overall yield of 6    from 1, including four column purifications, was 32%, and afforded a    ca. 1:1 mixture of α,β anomers.

A series of purine nucleoside analogs were prepared through the couplingof 6 and 2,6-dichloropurine. A Lewis acid catalyzed reaction utilizingstannic chloride in acetonitrile was found to be an efficient method toachieve this coupling, and 30 and 25% yields of α and β anomers of 7were obtained after chromatographic purification/separation. Aftertreatment with ethanolic ammonia to produce the respective blocked2-chloroadenine nucleosides 8α and 8β, removal of the O-benzyl groupswas accomplished with boron trichloride in dichloromethane at −50° C. toyield the nucleoside targets 9α and 9β. Treatment of 7α and 7β withsodium azide in 95% aqueous ethanol at reflux produced the corresponding2,6-diazido intermediates 10α and 10β, which were subjected to reductionwith stannous chloride in dichloromethane to afford the blockeddiaminopurine nucleosides 11α and 11β in good yields. Deblocking of 11αand 11β with boron trichloride in dichloromethane produced the targetdiamino nucleoside 12α and 12β. The conversion of 12β to thecorresponding guanine nucleoside 13 was accomplished by treatment withadenosine deaminase under standard conditions. Though the deaminationwas slow, it went to completion at room temperature in 72 hours.Cytosine, thymine and uracil were coupled with thiosugar 5 to afford 14α(31%), 14β (30%), 16αβ (60%) and 18αβ (70%) respectively, which weredeblocked by boron trichloride to give the nucleosides 15α (70%), 15β(70%), 17αβ (65%) and 19αβ (65%) respectively.

The pharmaceutically acceptable effective dosage of the active compoundof the present invention to be administered is dependent on the speciesof the warm-blooded animal (mammal), the body weight, age and individualcondition, and on the form of administration.

The pharmaceutical composition may be oral, parenteral, suppository orother form which delivers the compounds used in the present inventioninto the bloodstream of a mammal to be treated.

The compounds of the present invention can be administered by anyconventional means available for use in conjunction withpharmaceuticals, either as individual therapeutic agents or in acombination of therapeutic agents. They can be administered alone, butgenerally administered with a pharmaceutical carrier selected on thebasis of the chosen route of administration and standard pharmaceuticalpractice.

The dosage administered will, of course, vary depending upon knownfactors, such as the pharmacodynamic characteristics of the particularagent and its mode and route of administration; the age, health andweight of the recipient; the nature and extent of the symptoms, the kindof concurrent treatment; the frequency of treatment; and the effectdesired. A daily dosage of active ingredient can be expected to be about0.001 to 1000 milligram (mg) per kilogram (kg) of body weight, with thepreferred dose being 0.1 to about 30 mg/kg.

Dosage forms (compositions suitable for administration) typicallycontain from about 1 mg to about 100 mg of active ingredient per unit.In these pharmaceutical compositions, the active ingredient willordinarily be present in an amount of about 0.5-95% by weight based onthe total weight of the composition.

The active ingredient can be administered orally in solid dosage forms,such as capsules, tablets, and powders, or in liquid dosage forms, suchas elixirs, syrups, and suspensions. It can also be administeredparenterally, in sterile liquid dosage forms. The active ingredient canalso be administered intranasally (nose drops) or by inhalation. Otherdosage forms are potentially possible such as administrationtransdermally, via a patch mechanism or ointment.

Gelatin capsules contain the active ingredient and powdered carriers,such as lactose, starch, cellulose derivatives, magnesium stearate,stearic acid, and the like. Similar diluents can be used to makecompressed tablets. Both tablets and capsules can be manufactured assustained release products to provide for continuous release ofmedication over a period of hours. Compressed tablets can besugar-coated or film-coated to mask any unpleasant taste and protect thetablet from the atmosphere, or enteric coated for selectivedisintegration in the gastrointestinal tract.

Liquid dosage forms for oral administration can contain coloring andflavoring to increase patient acceptance.

In general, water, a suitable oil, saline, aqueous dextrose (glucose),and related sugar solutions and glycols such as propylene glycol orpolyethylene glycols are suitable carriers for parenteral solutions.Solutions for parenteral administration preferably contain awater-soluble salt of the active ingredient, suitable stabilizingagents, and, if necessary, buffer substances. Antioxidizing agents suchas sodium bisulfite, sodium sulfite, or ascorbic acid, either alone orcombined, are suitable stabilizing agents. Also used are citric acid andits salts and sodium EDTA. In addition, parenteral solutions can containpreservatives, such as benzalkonium chloride, methyl- or propylparaben,and chlorobutanol.

Suitable pharmaceutical carriers are described in Remington'sPharmaceutical Sciences, Mack Publishing Company, a standard referencetext in this field.

Useful pharmaceutical dosage forms for administration of the compoundsaccording to the present invention can be illustrated as follows:

Capsules

A large number of unit capsules are prepared by filling standardtwo-piece hard gelatin capsules each with 100 mg of powdered activeingredient, 150 mg of lactose, 50 mg of cellulose, and 6 mg of magnesiumstearate.

Soft Gelatin Capsules

A mixture of active ingredient in a digestible oil such as soybean oil,cottonseed oil, or olive oil is prepared and injected by means of apositive displacement pump into gelatin to form soft gelatin capsulescontaining 100 mu of the active ingredient. The capsules are washed anddried.

Tablets

A large number of tablets are prepared by conventional procedures sothat the dosage unit was 100 mg of active ingredient, 0.2 mg ofcolloidal silicon dioxide, 5 mg of magnesium stearate, 275 mg ofmicrocrystalline cellulose, 11 mg of starch, and 98.8 mg of lactose.Appropriate coatings may be applied to increase palatability or delayabsorption.

Various modifications of the invention in addition to those shown anddescribed herein will be apparent to those skilled in the art from theforegoing description. Such modifications are also intended to fallwithin the scope of the appended claims.

The foregoing disclosure includes all the information deemed essentialto enable those skilled in the art to practice the claimed invention.Because the cited applications may provide further useful information,these cited materials are hereby incorporated by reference in theirentirety.

The following non-limiting examples are presented to further illustratethe present invention. The NMR spectra reported in the examples belowwas determined by NOE difference spectroscopy.

EXAMPLE 1 Preparation of 2,3,5-Tri-O-benzyl-D-arabinose DibenzylDithioacetal (4)

D-Arabinose (1, 25 g, 167 mmol) was stirred for 5 hours in 0.5% hydrogenchloride in methanol (675 mL) at room temperature and then neutralizedwith Amberlite IRA-400 OH anion exchange resin. The filtrate andwashings were combined and evaporated to dryness and the crude productwas purified by silica gel chromatography (CHCl₃/MeOH, 92:8) to afford26.2 g of methyl D-arabinofuranoside (2, 95% yield) as an and (1:1)mixture. MS 164 (M)⁺.

To an ice-cold solution of 2 (10 g, 60.9 mmol) in dry tetrahydrofuran(350 mL) was added sodium hydride (60% dispersion in mineral oil, 14.8g, 370 mmol) and the reaction mixture was stirred for 15 min under N₂.To this reaction mixture was added solid tetrabutylammonium iodide (0.36g, 0.96 mmol) followed by a dropwise addition of benzyl bromide (36.6 g,214 mmol). The reaction mixture was stirred for 3 days at roomtemperature. After the addition of methanol (25 mL), the solution wasevaporated under reduced pressure, and the crude product was purified bysilica gel chromatography (cyclohexane/EtOAc, 9:1) to afford pure methyl2,3,5-tri-O-benzyl-D-arabinofuranoside (3, 23 g, 87% yield). MS 435(M+H)⁺.

To a solution of 3 (42 g, 97 mmol) in dichloromethane (1000 mL) wereadded benzyl mercaptan (49.6 g, 400 mmol) and stannic chloride (4.93 g,18.9 mmol), and the reaction mixture was stirred at room temperatureovernight. After neutralization with 5% aqueous NaHCO₃ (750 mL), theorganic layer was separated and the aqueous layer was extracted withdichloromethane (500 mL). The combined organic layers were evaporated,and crude 4 was purified by silica gel chromatography(cyclohexane/EtOAc, 99:1) to afford 4 (8.53 g, 63%) of sufficient purityto carry forward. MS 657 (M+Li)⁺.

EXAMPLE 2 Preparation of2,3,5-Tri-O-benzyl-1-O-acetyl-4-thio-L-xylofuranose (6)

To a solution of 4 (13.0 g., 20 mmol) in dry 2:1 toluene/acetonitrile(200 mL) were added triphenylphosphine (15.7 g, 60 mmol), iodine (12.7g, 50 mmol) and imidazole (5.44 g, 80 mmol). The reaction mixture wasstirred at 90° C. for 24 hours after which time the solution wasevaporated to dryness. The crude product was purified by silica gelchromatography (cyclohexane/EtOAc, 4:1) to afford benzyl2,3,5-tri-O-benzyl-1,4-dithio-L-Xylofuranoside as a syrup (5, 9.0 g,72%). MS 543 (M+H)⁺.

To a suspension of mercuric acetate (7.29 g, 22.9 mmol) in acetic acid(96 g) was added 5 (5.42 g, 10 mmol), and the resulting mixture wasstirred at room temperature for 2 h. The reaction mixture was dilutedwith dichloromethane (200 mL) and washed successively with water,saturated aqueous NaHCO₃ and 5% aqueous KCN solution. The organic layerwas dried over Na₂SO₄ and concentrated. Chromatography of the crudeproduct using cyclohexane:ethylacetate (98:2) as eluent gave a mixtureof and (1:1) anomers of 6 (3.73 g, 78%) as a colorless syrup. MS 479(M+H)⁺.

EXAMPLE 3 Preparation of 9-(2,3,5-Tri-O-benzyl-4-thio-α and-β-L-xylofuranosyl)-2,6-dichloropurine (7α and 7β)

To a stirred mixture of 6 (0.956 g, 2 mmol) and 2,6-dichloropurine(0.568 g, 3 mmol) in acetonitrile (50 mL) at room temperature was addeda solution of stannic chloride in dichloromethane (3 mL of 1.0 M) over 1min and stirring was continued for 2 hours. The reaction mixture wasquenched by pouring it into a mixture of 50 mL of dichloromethane and 25mL of saturated NaHCO₃. The organic phase was dried (MgSO₄) andconcentrated. The residue was purified by silica gel chromatography(cyclohexane/EtOAc, 9:1) to afford 7α (364 mg, 30%) eluting firstfollowed by 7β (291 mg, 25%).

-   Compound 7α: MS 608 (M+H)⁺.-   Compound 7β: MS 608 (M+H)⁺.

EXAMPLE 4 Preparation of 2-Chloro-9-(4-thio-α-L-xylofuranosyl)adenine(9α)

A mixture of compound 7α (608 mg, 1 mmol) and saturated ethanolicammonia (100 mL) was heated at 50° C. in a glass-lined stainless steelpressure vessel for 48 hours. The reaction mixture was evaporated todryness to afford a solid (8α) that was dissolved in dichloromethane (50mL) and was added dropwise to a solution of 1 M BCl₃ in CH₂Cl₂ (100 mL)at −50° C. Solid precipitated from the solution near the end ofaddition. The reaction in a tightly sealed flask was stored at −20° C.for 16 h. The resulting clear solution was evaporated to dryness at −20°C. to give a dark residue. A solution of this material in ice-coldCH₂Cl₂ (25 mL) was evaporated to dryness four times to provide a foam.Ice-cold saturated aqueous NaHCO₃ (20 mL) was added to the foam, and themixture was stirred vigorously until the pH remained stable (pH 7-8).Water (150 mL) was added to form a clear solution that was extractedwith two portions of CH₂Cl₂ (50 mL, 25 mL) to remove color andimpurities. The colorless aqueous layer was held briefly under vacuum toremove residual CH₂Cl₂ before being applied to a column (13×190 mm) ofBio Beads SM-4 (100-200 mesh) equilibrated in water. Water elution withfractions monitored at 254 nm provided pure 9α (175 mg, 55%); TLC,3:1:0.1 CHCl₃—MeOH—NH₄OH, R_(f) 0.55; m.p. 140 MS 318 (M+H)⁺.

EXAMPLE 5 Preparation of 2-Chloro-9-(4-thio-β-L-xylofuranosyl)adenine(9β)

The compound of this example was prepared from 7 by the same procedureas reported for 9β in 45% yield; TLC, 3:1:0.1 CHCl₃—MeOH—NH₄OH, R_(f)0.45; m p 235: MS 318 (M+H)⁺.

EXAMPLE 6 Preparation of9-(2,3,5-Tri-O-benzyl-4-thio-α-L-Xylofuranosyl)-9H-purine-2,6-diamine(11)

A solution of 7α (303 mg, 0.5 mmol) and sodium azide (162.5 mg, 2.5mmol) in mL of 95% ethanol was heated at reflux for 2 hours. The solventwas removed in vacuo, and the residue was partitioned betweendichloromethane and water. The organic phase was dried (MgSO₄) andconcentrated in vacuo to yield 290 mg of a yellowish solid (10α) [TLC:CHCl₃/MeOH, 97:3; Rf 0.45; mass spectrum, m/z 621 (M+H)+], which wasredissolved in 20 mL of dichloromethane and 2 mL of methanol. Thissolution was treated with stannous chloride (190 mg, 1 mmol) and theresulting suspension was stirred for 30 min. After evaporation ofsolvent, purification was accomplished by silica gel chromatography(CHCl₃/MeOH, 97:3) to afford 11α (214 mg, 75%), which was suitable fordeblocking. MS 569 (M+H)⁺.

EXAMPLE 7 Preparation of9-(2,3,5-Tri-O-benzyl-4-thio-β-L-Xylofuranosyl)-9H-purine-2,6-diamine(11β)

The compound of this example was prepared in 78% yield by the sameprocedure as reported above for 11α but starting from 7β, affordingmaterial suitable for deblocking. MS 569 (M+H)⁺.

EXAMPLE 8 Preparation of9-(4-Thio-α-L-Xylofuranosyl)-9H-purine-2,6-diamine (12α)

An ice-cold solution of 11α (218 mg, 0.38 mmol) in CH₂Cl₂ (2.6 mL) wasadded dropwise to a solution of 1 M BCl₃ in CH₂Cl₂ (30 mL) at −50° C.Solid precipitated from the solution near the end of addition. Thereaction in a tightly sealed flask was stored at −20° C. for 16 hours.The resulting clear solution was evaporated to dryness at −20° C. togive a dark residue. A solution of this material in ice-cold CH₂Cl₂ (25mL) was evaporated to dryness four times to provide a foam. Ice-coldsaturated aqueous NaHCO₃ (20 mL) was added to the foam, and the mixturewas stirred vigorously until the pH remained stable (pH 7-8). Water (150mL) was added to form a clear solution that was extracted with twoportions of CH₂Cl₂ (50 mL, 25 mL) to remove color and impurities. Thecolorless aqueous layer was held briefly under vacuum to remove residualCH₂Cl₂ before being applied to a column (13×190 mm) of Bio Beads SM-4(100-200 mesh) equilibrated in water. Water elution with fractionsmonitored at 254 nm provided pure 12α that was crystallized from hotMeOH (81 mg, 71%). TLC, 3:1:0.1 CHCl₃—MeOH—NH₄OH, R_(f) 0.48; m.p.140;MS 299 (M+H)⁺.

EXAMPLE 9 Preparation of9-(4-Thio-β-L-Xylofuranosyl)-9H-purine-2,6-diamine (12β)

The compound of this example was prepared in 75%yield (Crystallized fromwater) by the same procedure as reported above for 12α but starting from11β. TLC, 3:1:0.1 CHCl₃—MeOH—NH₄OH, R_(f) 0.43 M.p 130; MS 299 (M+H)⁺.

EXAMPLE 10 Preparation of 9-(4-Thio-β-L-xylofuranosyl)guanine (13)

To a solution of 12β (50 mg, 0.17 mmol) in 20 mL of water was added 100units of adenosine deaminase type VIII (40 μL). The reaction was stirredfor 72 hours, the solution was boiled for 3 min to deactivate theenzyme, and the suspension was treated with charcoal and filteredthrough Celite. The filtrate was concentrated to give gelatinous 13which was dissolved in hot water (4 mL) and filtered through 0.45 μmfilter (25 mm, Gelman Acrodisc GHP-GF). The clear filtrate waslyophilized to provide 13 as a fluffy white solid which was crystallizedfrom water (20 mg, 40%): TLC,3:1:0.1 CHCl₃—MeOH—NH₄OH, R_(f) 0.40; m.p.260; MS 300 (M+H)⁺.

EXAMPLE 11 Preparation of1-(2,3,5-Tri-O-benzyl-4-thio-L-Xylofuranosyl)cytosine (14α and 14β)

To a suspension of cytosine (1.27 g, 11.5 mM) in anhydrous acetonitrile(30 mL) was added BSA (5.48 g, 27 mM). The resulting mixture was heatedat 50° C. for 3 hours.

The mixture was cooled to room temperature and sugar 5 (2.53 g, 4.67 mM)was added followed by powdered 4A molecular seives (1.5 g) and NBS (1.78mg, 10 mM). The suspension was heated at reflux for 50° C. 18 hours andthen cooled to room temperature and filtered. Filtrate and washings wereevaporated to dryness and purified by silica gel column (Chloroform andEthylacetate 90:10) to afford 0.76 g (31%) of compound 14α and 0.75 g(30%) of 14β.

-   14α MS 530 (M+H)⁺.-   14β MS 530 (M+H)⁺.

EXAMPLE 12 Preparation of1-(2,3,5-Tri-O-benzyl-4-thio-α,β-L-Xylofuranosyl)thymine (16α,β)

To a suspension of thymine (2.0 g, 15.8 mM) in anhydrous acetonitrile(40 mL) was added BSA (8.23 g, 40.4 mM). The resulting mixture washeated at 50° C. for 3 hours. The mixture was cooled to room temperatureand sugar 5 (7.48 g, 13.8 mM) was added followed by powdered 4Amolecular seives (1.8 g) and NBS (2.66 g, 15 mM). The suspension washeated at reflux for 50° C. 18 hours and then cooled to room temperatureand filtered. Filtrate and washings were evaporated to dryness andpurified by silica gel column (Chloroform and Ethylacetate 90:10) toafford 4.51 g (60%) of compound 16 as 1:1 α,β mixture (1:0.85). MS 545(M+H)⁺.

EXAMPLE 13 Preparation of1-(2,3,5-Tri-O-benzyl-4-thio-α,β-L-Xylofuranosyl)uracil (18α,β)

To a suspension of Uracil (1.29 g, 11.5 mM) in anhydrous acetonitrile(30 mL) was added BSA (5.48 g, 27 mM). The resulting mixture was heatedat 50° C. for 3 hours. The mixture was cooled to room temperature andsugar 5 (2.53 g, 4.67 mM) was added followed by powdered 4A molecularseives (1.5 g) and NBS (1.78 mg, 10 mM). The suspension was heated atreflux for 50° C. 18 hours and then cooled to room temperature andfiltered. Filtrate and washings were evaporated to dryness and purifiedby silica gel column (Chloroform and Ethylacetate 90:10) to afford 1.73g (70%) of compound 16 as mixture (1:1). MS 531 (M+H)⁺.

EXAMPLE 14 Preparation of 1-(4-thio-α-L-Xylofuranosyl)cytosine (15α)1-(4-thio-β-L-Xylofuranosyl)cytosine (15β)1-(4-thio-α,β-L-Xylofuranosyl)thymine (17α,β)1-(4-thioα,β-L-Xylofuranosyl)uracil (19α,β)

Compounds 14α, 14β, 16α,β and 18α,β were deblocked as disclosed abovefor 12 to afford compound 15α (70%) and 15β (70%); MS 259 (M+H)⁺);17α,β, (65% yield,MS 274 (M+H)⁺); and 19α,β, (65% yield, MS 260(M+H)respectively.

Biological Data

The cell culture cytotoxicity of compounds of the present invention wasdetermined against several different human cancel cell lines (see Table1 below) and for antiviral activity (see Table 2 below).

TABLE 1 Cytotoxicity data: IC50 (μM) CCRF- NCI- com- CEM CAKI-1 DLD-1H23 SK-MEL-28 SNB-7 pound (leukemia) (renal) (colon) (lung) (melanoma)(CNS)  9α >100 >100 >100 >100 >100 >100 9β >100 >100 >100 >100 >100 >100 12α >100 >100 >100 >100 >100 >10012β >100 >100 >100 >100 >100 >100 13 >100 >100 >100 >100 >100 >100 15α8.0 >100 >100 >100 >100 >100 15β 11.0 >100 >100 >100 >100 9017αβ >100 >100 >100 >100 >100 >100 19αβ >100 >100 >100 >100 >100 >100

TABLE 2 Antiviral (CMV) data compound IC50 TC50 TI Ganciclovir  8.6μM >10 μM >11.6  12α 0.051 μM >10 μM >196.1 15β 0.022 μM >10 μM >454.515α 0.026 μM >10 μM >384.6 IC 50: 50% Inhibitory Concentration of CMV TC50: Toxic Concentration at 50% cell viability TI: Therapeutic Index(TC50/IC50)

1. Compound represented by the formula 1:

wherein each R individually is H, or an acyl group; A is selected fromthe group consisting of

wherein Y is X₁, N₃, NH₂, monoalkylamino or dialkylamino; Z is O or S;and X is selected from the group consisting of hydrogen, halo, hydroxy,alkoxy, alkyl, haloalkyl, alkenyl, haloalkenyl, alkynyl, amino,monoalkylamino, dialklamino, thioaryl, thioalkyl, allylamino, cyano andnitro; tautomers thereof; and pharmaceutically acceptable salts thereof,and wherein said compound is in the L-xylo configuration.
 2. Thecompound of claim 1 wherein Y is NH₂.
 3. The compound of claim 1 whereinX is chlorine.
 4. The compound of claim 1 wherein R is H.
 5. Thecompound of claim 1 wherein A is


6. The compound of claim 1 being selected from the group consisting of2-chloro-9-(4-thio-α-L-xylofuranosyl)adenine;9-(2,3,-tris-O-benzyl4-thio-α,L-xylofuranosyl)-9H-purine-2,6-diamine;9-(4-thio-α-L-xylofuranosl)-9H-puriuo-2,6-diamine,9-(4-thio-β-L-xylofuranosyl)guanine;1-(2,3,5-tri-o-benzyl-4-thio-α,β-L-xylofuranosyl)thymine;1-(2,3,5-tri-O-benzyl-4-thio-α,β-L-xylofuranosyl)uracil;1-(4-thio-α,β-L-xylofuranosyl)thymine;1-(4-thio-α,β-L-xylofuranosyl)uracil;1-(2,3,5-tri-O-benzyl-4-thio-α,β-L-xylofuranosyl)cytosine; and1-(4-thio-α,β-L-xylofuranosyl)cytosine.
 7. A pharmaceutical compositioncomprising a compound according to claim 1 in an amount effective as ananticancer agent.
 8. The compound of claim 1 being2-chloro-9-(4-thio-α-L-xylo-furanosyl)adenine.